The Role of Environmental Hazards in Premature Birth Workshop Summary (2003) / Chapter Skim
Currently Skimming:
Abstracts
Abstracts
Pages 77-106
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 77... ...
at NIEHS strives to safeguard public health by identifying and characterizing the toxic effects of environmental chemicals and by providing quality data that regulatory agencies can use for risk assessments. NTP tests that assess reproductive toxicity include (1)
|
From page 78... ...
It may be necessary to modify some of the current NTP reproductive test protocols to better collect this information. However, considering the infrequent observation of a significant effect, especially a shortening of gestation that might be associated with "preterm delivery, one has to question whether it would be worth the associated increased test cost.
|
From page 79... ...
Our histological studies of implantation sites from NK cell-deficient strains, modified in different genes, showed that no uNK cells were present and that the architecture of implantation sites was disturbed. In particular, the decidual spiral arteries did not undergo the physiological changes of pregnancy and the decidua was hypocellular.
|
From page 80... ...
Histological specimens from implantation sites are evaluated for numbers of uNK cells, their stages of maturity (granularity and cell diameter) , and their distribution relative to the decidual spiral arteries in comparison to controls.
|
From page 81... ...
REGULATION AND ASSESSMENT OF UTERINE CONTRACTILITY AND CERVICAL RIPENING DURING PREGNANCY R.E. Garfield The problems associated with labor during pregnancy are among the most important health issues facing health care providers of women.
|
From page 82... ...
The potential benefits of the proposed instrumentation and methods include quantitative procedures to predict the onset and progress of the preparatory steps leading to normal or preterm labor, reduction in the rate of preterm delivery, improvement in maternal and perinatal out
|
From page 83... ...
In parturition the type 2 isomer of prostaglandin H synthase (PGHS-2) is particularly important and its expression has been found to increase in term and preterm labor.
|
From page 84... ...
The latter two categories taken together are often called spontaneous preterm birth. Approximately 20 percent of preterm births are indicated, approximately 30 percent follow spontaneous rupture of the membranes, and approximately 50 percent follow spontaneous preterm labor.
|
From page 85... ...
As stated earlier, intrauterine infection is associated with a very large proportion of the earliest preterm births. Often, this intrauterine infection is linked to the presence of bacterial vaginosis, which, in nearly 20 studies, is associated with an approximately twofold increased risk of a preterm birth.
|
From page 86... ...
The use of antibiotics in women in early preterm labor in an attempt to reduce preterm delivery has more often than not been unsuccessful. There are, however, two randomized studies, both using metronidazole and ampicillin, that suggest benefit.
|
From page 87... ...
Rowland Hogue Although stressful events and lack of social support during pregnancy have been associated in some studies with increased risk of preterm delivery, interventions to increase social support have, in general, not lengthened gestation. Lack of effect may suggest that the causal hypothesis is faulty.
|
From page 88... ...
Potential risk factors for host susceptibility may include factors present at birth or related to personality, early life experiences, coping strategies, and circumstances of the pregnancy. In this framework, external resources available for coping with stress, such as levels of social support, are part of the environmental context.
|
From page 89... ...
Testing protocols for reproductive and developmental toxicity evaluation of pesticides and industrial chemicals include evaluations of gestation length and of survival, growth, and development of offspring. Recent changes in the prenatal developmental toxicity testing protocol further increase the possibility of detecting alterations in gestation length.
|
From page 90... ...
Alterations in gestation length appear to be effects that occur at higher dose levels, with effects on offspring survival, birth weight, or other measures of growth and development as more sensitive indicators of reproductive and developmental toxicity. ASSESSMENT AND RELEVANCE OF ENVIRONMENTAL CHEMICAL EFFECTS ON UTERINE MUSCLE Rita Loch-Caruso Although regulation of uterine contractility is fundamental for successful pregnancy, relatively little attention has been given to environmental chemical effects on the uterine muscle.
|
From page 91... ...
These results suggest that some environmental chemicals may directly stimulate uterine contraction by activating calcium-dependent mechanisms. In addition, prolonged exposure to the estrogenic PCB 4-hydroxy-2',4',6'-trichlorobiphenyl increased oxytocin-induced oscillatory uterine contraction frequency in an estrogen receptor-dependent manner, showing the potential for estrogenic environmental chemicals to stimulate uterine contractions via indirect mecha.
|
From page 92... ...
. Risk factors that have been studied and appear not to be associated with increased risk of preterm birth were chlorinated water disinfection by-products and use of video display terminals.
|
From page 93... ...
. Clearly, knowledge of the mechanisms that control the process of myometrial activation is central to the development of strategies to prevent preterm labor.
|
From page 94... ...
Continued hypoxic stimulation would eventually lead to cortisol induction of placental endocrine changes, myometrial activation, and the initiation of preterm labor with the birth of a baby that is small for its gestational age. Multifetal pregnancies are known to be at increased risk of preterm birth.
|
From page 95... ...
A switch in myometrial contractility pattern from contractures to con2. Rupture of the fetal membranes, and 3.
|
From page 96... ...
This presentation compares the evidence of fetal involvement in rhesus monkey pregnancy and sheep pregnancy. Evidence for increased fetal adrenal function in late gestation.
|
From page 97... ...
Continuous infusion of androstenedione into the pregnant rhesus monkey at 0.8 of gestation produces labor associated with the three indispensable processes described above: a switch of myometrial contractures to contractions, rupture of the fetal membranes, dilation of the cervix, and delivery of live young (Nathanielsz et al., 1998~. It is interesting to note that although the infusion of androgen was continuous and the maternal plasma estrogen concentration was elevated throughout the 24-hour day, the switch from contractures to contractions occurred only around the hours of darkness.
|
From page 98... ...
TOXIC SOCIAL ENVIRONMENT: A FACTOR IN PRETERM BIRTH? Janet Rich-Edwards Two of the largest and most intractable risk factors for preterm birth are maternal social class and race or ethnicity.
|
From page 99... ...
CAUSES AND MECHANISMS OF PREMATURE LABOR James M Roberts This presentation reviews the currently popular theories of preterm labor to provide insight as to where toxicants could act to lead to preterm birth.
|
From page 100... ...
However, current thinking has largely abandoned the concept of an abnormal biological clock mechanism in favor of distinct factors stimulating term and preterm birth. Our level of understanding the mechanisms of preterm labor, however, does not justify abandoning this (or any)
|
From page 101... ...
It is quite probable that all preterm labor is not from a single cause and that all of the currently suggested precursors of preterm birth (and likely others) are important in different women and may be interactive.
|
From page 102... ...
, and psychological stress has been conducted for some time and offers insights into methodologic challenges, suggests possible etiologic pathways, and identifies potential confounding factors that must be considered. At present, strong predictors of preterm birth are limited to multiple gestation, prior preterm birth, and African-American ethnicity; weaker but modifiable influences include infection, tobacco use, low prepregnancy weight, lower socioeconomic status, and other prior adverse pregnancy outcomes.
|
From page 103... ...
For example, there are consistent findings of an association between cocaine use and preterm birth, reduced risk associated with leisure time physical activity during pregnancy, reduced risk with favorable nutritional status and use of prenatal vitamins, and increased risk associated with physically demanding occupations, yet none are necessarily causal, and isolating a true etiologic effect from a spurious association due to other unmeasured or unknown factors has been unsuccessful thus far. Isolating environmental agents from the circumstances that give rise to exposure will pose a serious challenge for the many environmental agents associated with socioeconomic deprivation and less favorable life-styles.
|
From page 104... ...
Some risk factors may be shared across spontaneous and indicated preterm births, whereas others are likely to differ. Other divisions of preterm birth are based on clinical presentation (idiopathic preterm labor, preterm premature rupture of membranes)
|
From page 105... ...
However, more studies are needed and multidisciplinary collaborations are required in order to jointly and comprehensively assess the role of environmental factors, genetic factors, and gene-environment interactions in preterm delivery among populations with marked differences in social status and environmental exposures. ROLE OF NITRIC OXIDE IN UTERINE ACTIVITY AND PREMATURE PARTURITION ChandraseLhar Yallampalli Preterm labor and delivery remain an important problem in obstetrics, with prematurity contributing to 8-10 percent of neonatal deaths and responsible for 60-70 percent of neonatal morbidity in the United States.
|
From page 106... ...
The effects of GTN appeared to be due to reductions in uterine contractions in these preterm labor women. It is unknown from these studies whether NO donors are superior to other tocolytics; however, the side effects appear to be less severe.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.